1. Field of the Invention
The present invention pertains to wavelength routers for use in fiber optic communications systems and, more particularly, to a wavelength router for directing discrete channels in a wavelength division multiplexed (WDM) optical signal to select output optic ports.
2. Description of the Related Art
Wavelength routers have many applications in WDM networks and can be used, for example, as a single input port device to demultiplex wavelength channels. Such routers can also be used as a multi-input device 10 as shown in FIG. 1 for providing wrap-around routing to output ports, as is known in the art, and for interconnecting nodes of a network. For example, device 10 in FIG. 1 has an equal number of input ports 12 (shown as A, B, C, and D) and output ports 14. When a WDM signal xcex having wavelengths xcex1, xcex2, xcex3, xcex4 is input to the router through input fiber A, the wavelengths are routed, as shown, such that xcex1 is output on output fiber 14A, xcex2 on output fiber 14B, etc. For wrap-around routing the input signal xcex is provided on a different input port (e.g. port 12B), in which case output port 14B receives channel xcex1, output port 14C receives xcex2, output port 14D receives xcex3 and output port 14A receives xcex4.
Presently, Nxc3x97N routers having an equal number of input ports, output ports and wavelengths are constructed using a planar waveguide structure such as an arrayed waveguide grating or Dragone router. Such routers, however, do not operate with multimode fibers or multimode waveguide systems, thereby limiting their utility in local area network applications. Moreover, such routers do not accommodate broad wavelength channels, thus requiring the use of costly narrow and precise lasers for proper operation.
The present invention is directed to a multi-port wavelength router for directing a WDM optical signal having a plurality of adjacent-in-wavelength channels to select output ports. The WDM signal is provided by or to an input port, which is preferably a linear array of optic fibers, and is directed to a lens. The lens collimates the received WDM signal onto a planar grating which demultiplexes the channels in a first direction by providing angular separation along a first direction to the channels as a function of the channel wavelengths. The demultiplexed signal is directed back through the lens for focusing and then provided to an array of optical elements. The optical element array is positioned so that each element receives a channel, imparts to that channel a spatial displacement along a second direction, and directs the displaced channel back through the lens for re-collimation on the grating. The first direction angular displacement is cancelled out by the grating through the second pass and the spatially displaced channels are then reflected back to the lens which focuses the channels to the output ports. In this embodiment, a linear array of input fibers oriented along the first direction can be used to rout the discrete channels to a two-dimensional array of output fibers.
In another embodiment, an Nxc3x97N router having an equal number of output ports and input ports is realized by providing an additional second displacement to the channels in a direction angularly offset from the second direction. This is accomplished through use of a reflective element which causes a second pass to occur through the router before the displaced channels are provided to the output ports.
As an alternative to a second pass through a single router, a second router stage positioned at an angle relative to the optical axis of the first router stage may be employed. This further embodiment allows the use of a planar surface device, such as a modulator or add/drop element, disposed between the two router stages to thereby allow for selective manipulation of the individual channels.